Abstract

We have earlier presented theoretical and experimental results demonstrating that the nonresonant third order optical susceptibility χ⁽³⁾(−ω;ω,ω,−ω) can be enhanced for nonlinear optical processes originating from real population of electronic excited states in conjugated linear chains[1,2]. Compared with the ground state, χ⁽³⁾(−ω;ω,ω,−ω) of π-conjugated linear chains can be enhanced by orders of magnitude when the first S₁ or second S₂ π-electron excited state is optically pumped and then populated for times long enough to perform nonresonant measurements of χ⁽³⁾(−ω;ω,ω,−ω) at frequencies different from the resonant pump frequency. In this paper, a dynamical model is developed for the time evolution of the nonresonant microscoopic degenerate four wave mixing (DFWM) susceptibility γ(-ω;ω,ω,-ω) for the excited state enhancement mechanism. The model is applied to the case of the six site chain, diphenylhexatriene (DPH).

© 1993 Optical Society of America